When Mort said "Hello", it sounded like the way he said "Hello" in Launchtime.

The Blue Danube Waltz was played when thelemurs were burping up gas for the rocket.

Kowalski and the rest of the penguin crew think that fish and churros are the greatest foods in the world.

King Julien's birthday could be in the summer since he mentioned his birthday after the summer conditions occurred. In Happy King Julien Day! he has a birthday on the 15th, that means his birthday is either on June 15th or August 15th, because Marlene mentioned that isn't July.

except King Julien Day is not Julien's birthday, it is a separate holiday to celebrate his awesomeness (this is also confirmed in Whispers and Coups when Julien lists off the days that would give Maurice reason to throw him a party, naming both his birthday and King Julien Day, proving they are two different holidays)

Julien is the 4th character to inflate to an enormous size. 1st is Kowalski, 2nd is Skipper, and the 3rd is Rico.